A background art of the present invention will be described by taking an excavator shown in FIG. 9 as an example.
The excavator includes a lower traveling body 1, an upper swirling body 2 mounted pivotally thereon and having an upper frame 3 as a base, various facilities and equipment including a cabin 4 mounted on the upper frame 3, a working attachment (or a excavation attachment) 5 attached to a front part of the upper frame 3, and a counterweight 6 attached to a rear end part of the upper frame 3. The cabin 4 is provided at a left-side front part in a traveling direction of the upper frame 3. An engine room 8 which houses the engine 7 is provided at a rear part of the upper frame 3.
FIG. 10 is a schematic cross-sectional view of arrangement of equipment and a flow of air in the engine room 8, as viewed from a rear side. The engine room 8 includes a long space in a left and right direction surrounded by a bottom plate 9 that is a part of the upper frame 3 and configures a floor of the engine room 8 and an engine guard member 10 which is formed of a panel material. The counterweight 6 is also a part of the engine guard member 10.
The engine 7 is installed in the engine room 8 in a posture extending in a left and right direction. At one side (a right side in the illustrated example) of right and left sides of the engine 7, a heat exchanger 11 including a radiator and an oil cooler for cooling the engine 7 and a fan 12 of an axial flow type are provided. An intake port 13 is provided on a right side portion of an upper wall of the engine room 8, and an exhaust port 16 is provided on a left side portion thereof. The fan 12 is rotated to draw in outside-air through the intake port 13, causing the air to pass through the heat exchanger 11, thereby cooling the heat exchanger 11.
At the other side (the left side in the illustrated example) of the left and right sides of the engine 7, a hydraulic pump 14 and a pump cover 15 positioned over the hydraulic pump 14 are provided. The pump cover 15 covers at least a part of the hydraulic pump 14 so as to prevent oil leaked and scattered in a mist shape from the hydraulic pump 14 from falling on the engine 7, specifically, on an exhaust system including a muffler not shown.
The rotation of the fan 12 forms a flow of air as indicated by arrowheads in FIG. 10 on a downstream side of the fan 12. The flow of air includes respective direction components in a rotational direction and a centrifugal direction of the fan 12, and the air moves from right to left in a long distance over substantially a whole region on the downstream side of the fan 12, and reaches the exhaust port 16 at a left end. The flow of air is therefore susceptible to large resistance and likely to form turbulence. This involves a decrease in exhaust efficiency.
As a technique for solving this problem, Patent Documents 1 and 2 disclose providing a groove, that is, a concave path, vertically extending to a portion behind a fan in front of the counterweight 6 forming a rear surface of the engine room 8, and directly collecting air blown out from the fan 12 to directions including a swirling direction and a radial direction of the fan 12, through the groove, and discharging the air outside the engine room; however, this technique does not actually improve exhaust efficiency of the air for the following reason. The air flowing as described above actually moves while swirling a whole region of a fan downstream side due to the component in a fan axial direction as described above. On the other hand, according to the prior art described in Patent Documents 1 and 2 above, only the air blown out from the fan 12 to the radial direction and the swirling direction is captured and discharged; air having passed through a majority of a region at the fan downstream side, therefore, cannot be collected. Furthermore, there is great airflow resistance in the inlet portion of the groove, which degrades air volume performance.
In the prior-art technique, it is possible to widen an air capturing range in the fan axial direction by increasing a groove width, in order to increase the air volume performance; however, the expansion of the groove width must be significantly constrained because the expansion thereof degrades the original function of the counterweight.
Patent Document 1: Japanese Patent Application Publication No. 2005-36447
Patent Document 2: Japanese Patent Application Publication No. 2005-145114